Tissue expanders are commonly used in breast reconstruction and scar revision surgery. Tissue expanders are placed beneath muscle or skin to expand the tissues and allow for the stretching, recruitment and creation of new skin and tissue. The tissue expander is filled with saline solution through a peripheral infusion port.
Conventionally, the infusion port is now integrated on the tissue expander with a magnetic metal backing both to allow for magnetic identification of the expander port and to prevent perforation or rupture of the expander by preventing the needle from puncturing the deep surface. Chemotherapy and other medication infusion devices also have metal backed ports for similar reasons.
A representative magnetic infusion port is disclosed in Rehder et al U.S. Pat. No. 6,588,432, which is incorporated herein by reference. FIGS. 1A and 1B show a magnetic infusion port 10 integrated on a tissue expander 18, as disclosed in the Rehder '432 Patent. As shown in FIGS. 1A and 1B, a needle guard member 12 is positioned spacially from and on the opposite side of the infusion port body 14 from where the needle 16 enters, to prevent the needle from puncturing the infusion port 10 and entering into the tissue expander 18 of the patient. A magnetic material 20 is affixed in the infusion port body outside the infusion port cavity 22 and the needle guard member 12. The magnetic material 20 is positioned outside the infusion port cavity 22 so that its placement does not interfere with the normal and proper insertion of a needle 16 into the infusion port cavity 22. The magnetic material 20 may be any shape or dimension, and made of any magnetically detectable material. For example, the magnetic material 20 may include samarium cobalt or neodymium iron boron, a combination thereof or like material. The outermost perimeter of the magnetic material 20 is spatially aligned with or within the perimeter of the region of the infusion port 10 into which the needle is injected, thus demarcating this region as a target for the needle 16. The magnetic material 20 also has a surface treatment to prevent it from corroding, such as a nickel coating or the like, and is completely enclosed in a polymer, such as a silicone elastomer or the like, to protect it from environmental exposure.
As further described in Rehder '432 Patent (and as shown in FIGS. 2A and 2B), to locate the infusion port 10, a magnetic detection probe 24 is used. The magnetic probe 24 has a polarity opposite to the polarity of the magnetic material 20 of the infusion port that faces the infusion port cavity 22. The magnetic probe 24 is therefore attracted to the magnetic material 20 of the port 10. In use, the probe 24 is scanned across the region of skin containing the port 10. The probe 24 will point to the magnetic material 20 and thereby pivot from a tilted position (when on one side of the magnetic material 20), to an upright position (when over the magnetic material 20, to an opposite tilted position (when on the opposite side of the magnetic material 30). When scanned along an x-axis, and then along a y-axis, the tilt of the probe 24 establishes at least four points of reference A, B, C, D creating a coordinate system. The location for inserting the needle is at the intersection I of two line segments L1 and L2, each defined by a pair of the reference points A and B/C and D established by two passes of the detection probe 24. This intersection I is where the magnetic infusion port 10 is located and where the needle 16 should enter.
FIGS. 3A and 3B show a typical detection probe 24 in use in association with a magnetic infusion port 10 on a tissue expander 18. FIG. 3A shows the probe 24 in a generally vertical position, pointing to the magnetic material 20 of the infusion port 10, indicating that it is magnetically aligned over the magnetic material 20 of the infusion port 10. FIG. 3B shows the probe 24 in tilted position, indicating that it is spaced to a side of the magnetic material 20 of the infusion port 10. The direction of the tilt points to the location of the infusion port 10.
The detection probe 24 used to locate the infusion port 10 adds to the expense of the expansion device 18. Also, in use, the detection probe 24 can be cumbersome to handle. The probe 24 can often stick and lead to inaccurate needle placement. This can, in turn, lead to the accidental perforation of the expander 18 if the needle is not directly introduced into the port 10 or otherwise perforates the silicone shell of the expander 18 at the wrong angle. If the expander 18 is not fully expanded for an adequate time when the expander 18 is prematurely punctured, this may necessitate a less than optimal result or another unnecessary operation to replace the expander 18.
Accurate and precise location of the infusion port 10 as close to its center as possible is critical. Often times the expander 18 is placed very deep to the skin with overlying muscle or fatty tissue. The deeper the expander 18 is in the body, the more difficult it is to identify with the probe 24.